When the omicron variant First emerging last November, many doctors, researchers and scientists hoped the new strain – although more transmissible – would cause fewer deaths.
Indeed, early research suggested that although the omicron spreads much faster than the delta variantit seemed to cause less severe illness.
But in Massachusetts, omicron had a much more deadly impact than delta – and in a shorter period of time. This is according to a study published Friday in the Journal of the American Medical Association.
The results illustrate that a highly contagious virus – even if it tends to cause milder disease – can still confer a significant number of deaths, said study lead author Dr Jeremy Faust, an emergency physician. at Brigham and Women’s Hospital in Boston.
“Even if we have a future wave where we are told that this version of the virus may be milder from person to person, we cannot afford to misinterpret this to mean that it cannot be extremely detrimental,” Faust said.
In the study, researchers from Brigham and Women’s Hospital and other institutions compared the number of excess deaths during the first eight weeks of the omicron wave in Massachusetts to the entire 23-week period of the l delta wave in the state.
Excess deaths – how many more people have died than would generally be expected in a given amount of time – have been seen as a more comprehensive measure of deaths caused, directly or indirectly, by the virus than just looking at confirmed deaths from Covid-19.
Researchers found that 2,294 additional deaths occurred during the omicron wave in Massachusetts from late December to mid-February, compared to 1,975 additional deaths in the state during the delta wave from late June to early December.
Excess deaths were seen in all adult age groups during the omicron wave, the researchers said, although people aged 65 and over had the most excess deaths of all age groups. ‘age.
Faust noted that a small number of deaths during the omicron wave could have been caused by delta infections that occurred several weeks earlier. In other words, a person could have been infected with the delta variant at the end of November, but only died at the end of December, when omicron took over.
The research has limitations: The data, which is preliminary, was only for Massachusetts, which means the results may not extend to other states, where demographics and Covid vaccine rates may differ. About 80% of the population of Massachusetts has received two doses of a vaccine, according to state data.
And data alone cannot explain why Massachusetts, among the states with the highest Covid vaccination rates, saw a higher than expected number of deaths during the omicron wave compared to the delta.
Nationally, excess deaths during the delta wave (about 266,000) still exceed those during the omicron (about 143,000), said Dr. Robert Anderson, chief of the mortality statistics branch at the Centers for Disease Control and Prevention from the National Center for Health Statistics. He did not participate in the research.
Anderson noted that calculating excess deaths attributed to delta versus omicron, both regionally and nationally, can be “difficult” because researchers must decide “when do we end the delta wave and where do we start the omicron wave”.
Which variant caused the most excess deaths can fluctuate by region — in New England, excess deaths during the delta wave tend to be lower than in other parts of the United States, Anderson added.
But in the South, especially in states like Alabama, Florida, Mississippi and Texas, excess mortality recorded during the delta wave tend to be higher, he said.
Bill Hanage, an associate professor of epidemiology at Harvard’s TH Chan School of Public Health who was not involved in the research, said the higher number of excess deaths during the omicron wave in Massachusetts may reflect the measures of attenuation of the state in place during the delta wave.
The combination of high vaccination rates and mitigation measures in Massachusetts means few people have been infected with Delta and therefore fewer people have died, he said.
But those same preventative tactics may not have been enough against the highly contagious omicron variant, Hanage said. (Studies have shown that two doses of a Covid vaccine provide minimal protection against omicron infection, although a booster injection may restore some of this protection.)
“And that led, perhaps unsurprisingly, to greater mortality, even though each of those infections was milder than it would have been had they been delta infections,” he said. .
Hanage also said the extent to which omicron appears milder compared to previous variants may be exaggerated by the high level of population immunity in the United States, which includes both vaccination and previous infections.
He published an article in the New England Journal of Medicine in February, which argued that the milder symptoms seen in omicron infections are likely due to more existing immunity, rather than the virus itself. In other words, by the time omicron arrived, more Americans had already been vaccinated or infected compared to previous waves.
However, even though omicron is truly milder, data from Massachusetts shows “that even something that people have come to think of as quite mild can, in fact, kill huge numbers of people.”
Faust, the study’s author, said people — especially those at higher risk of serious illness — should continue to enforce safety measures such as wearing masks indoors.
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